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Bouncy Castle Java CVE-2026-59639

| EUVDEUVD-2026-52035 HIGH
Improper Verification of Cryptographic Signature (CWE-347)
2026-08-03 bcorg GHSA-r3rc-x3pq-jmw7
Java Information Disclosure Jwt Attack Bc Java Bc Lts Java Bc Fja
8.7
CVSS 4.0 · Vendor: bcorg
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Severity by source

Vendor (bcorg) PRIMARY
8.7 HIGH
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber
vuln.today AI
7.5 HIGH

Network-reachable API, no privileges or user interaction required; integrity-only impact as attacker bypasses signature verification with no confidentiality or availability consequence.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
SUSE
MEDIUM
qualitative

Primary rating from Vendor (bcorg).

CVSS VectorVendor: bcorg

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
X

Lifecycle Timeline

3
Source Code Evidence Fetched
Aug 03, 2026 - 01:37 vuln.today
Analysis Generated
Aug 03, 2026 - 01:37 vuln.today
CVE Published
Aug 03, 2026 - 00:56 cve.org
HIGH 8.7

DescriptionCVE.org

In Bouncy Castle for Java before 1.85, CMS verifySignatures returns true for SignedData with zero signers. This issue also affects Bouncy Castle for Java LTS before 2.73.12, and Bouncy Castle for Java FIPS (BC-FJA) before bcpkix-fips 1.0.12 (1.0.X series), 2.0.12 (2.0.X series) and 2.1.12 (2.1.X series).

AnalysisAI

Signature bypass in Bouncy Castle for Java allows any attacker-supplied content wrapped in a zero-signer CMS envelope to pass CMSSignedData.verifySignatures() without any valid cryptographic signature. The method iterates an empty signerInfos SET, falls through to a vacuous return true, and any application using it as its top-level authenticity check silently accepts unsigned attacker-controlled content as authenticated - a classic fail-open flaw (CWE-347). …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Identify application accepting CMS SignedData input
Delivery
Craft degenerate SignedData with empty signerInfos SET
Exploit
Embed arbitrary payload in the envelope
Execution
Submit to application verification endpoint
Persist
verifySignatures() iterates zero signers and returns true
Impact
Unsigned content accepted as cryptographically authenticated
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Vulnerability AssessmentAI

Exploitation Exploitation requires: (1) the target application uses Bouncy Castle's CMSSignedData.verifySignatures() as its primary or sole authenticity check for received CMS/PKCS#7 SignedData - applications using lower-level SignerInformation APIs directly or other libraries are not affected; (2) the attacker can supply a crafted CMS envelope to that code path, e.g., via file upload, API call, or network protocol message carrying signed content. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 4.0 score of 8.7 (AV:N/AC:L/AT:N/PR:N/UI:N/VI:H) correctly captures the ceiling risk: zero privileges, zero complexity, network-reachable, and high integrity impact for any affected application using verifySignatures() as a trust boundary. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker targeting a firmware update service, document signing platform, or credential validation endpoint that uses CMSSignedData.verifySignatures() constructs a CMS SignedData envelope with an empty signerInfos SET wrapping arbitrary malicious payload. The envelope is submitted to the application's verification endpoint; verifySignatures() iterates zero signers and returns true, causing the application to accept and process the unsigned payload as fully authenticated. …
Remediation Upgrade to Bouncy Castle for Java 1.85 or later, Bouncy Castle LTS 2.73.12 or later, or bcpkix-fips 1.0.12 / 2.0.12 / 2.1.12 or later (matching the release series in use). … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours, identify and catalog all applications and services using Bouncy Castle for CMS/PKCS#7 signature verification, with particular focus on production systems and those processing regulated or security-sensitive content. …

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Threat intelligence, references, and detailed analysis are available after sign-in.

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Vendor StatusVendor

SUSE

Severity: Moderate
Product Status
SUSE Linux Enterprise Desktop 15 SP7 Affected
SUSE Linux Enterprise High Performance Computing 15 SP7 Affected
SUSE Linux Enterprise Module for Development Tools 15 SP7 Affected
SUSE Linux Enterprise Server 15 SP7 Affected
SUSE Linux Enterprise Server 16.0 Affected

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CVE-2026-59639 vulnerability details – vuln.today
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